Computers accept human user input in various ways. One of the most common input devices is the keyboard. Additional types of input mechanisms include mice and other pointing devices. Although useful for many purposes, keyboards and mice (as well as other pointing devices) sometimes lack flexibility. For example, many persons find it easier to write, take notes, etc. with a pen and paper instead of a keyboard. Mice and other types of pointing devices do not generally provide a true substitute for pen and paper.
Electronic tablets or other types of electronic writing devices offer an attractive alternative to keyboards and mice. These devices typically include a stylus with which a user can write upon a display screen in a manner similar to using a pen and paper. In some embodiments, a digitizer nested within the display converts movement of the stylus across the display into an “electronic ink” representation of the user's writing. The electronic ink is stored as coordinate values for a collection of points along the line(s) drawn by the user. Software may then be used to analyze the electronic ink to recognize shapes, gestures, characters, or sequences or characters such as words, sentences, paragraphs. In many cases, the recognized shapes may be converted to Unicode, ASCII or other code values for what the user has written. In other instances, a stylus may be used to “select” or otherwise interact with buttons or other graphical representations on the writing device. Increasingly, such touchscreen displays have been widely used in computer terminal applications, such as with portable and hand-held computers and with informational and point-of-purchase terminals, eliminating the need for less portable input devices, such as keyboards.
Generally, these touchscreen displays comprise a touch-sensitive or electromagnetic panel, which reports the two-dimensional touchpoint location (that is, the X axis and the Y axis) at which it has been touched, coupled to a display, which may show icons or buttons to be “selected” for data entry. However, proper operation of the touchscreen display requires calibration of the panel coordinates to corresponding points on the display.
Proper calibration is necessary in order to reliably determine the precise coordinates of the point at which the screen is touched or otherwise activated. In most cases, icons or symbols on the touchscreen display are sized and spaced according to the relative size of the touching member (typically, either a finger or a stylus), allowing some tolerance for error. However, there can be instances where it is important that X-Y coordinates of a touch location be very closely pinpointed. Moreover, there can be instances where poor calibration can lead to inaccurate data entry or can cause a customer or employee to be misunderstood or frustrated by what seems to be incorrect or unintended response to a screen entry.
Most current calibration techniques prompt a user to touch two or more reference points on the touchscreen. These points are then used to calibrate the coordinates of the panel to its underlying display. The actual coordinates at which the user touches the screen for calibration provides one or more “touchpoints” that serve as reference points for this positional calibration. The system stores these calibration touchpoints and performs any necessary scaling and coordinate adjustment based on these touchpoints. Unfortunately, these programs often require the user to stop performing their tasks and undergo the calibration procedure. Moreover, switching users may require further calibration of the writing surface.
For example, in some styluses, the emitting EM field that registered the “touching” with the writing surface is located not in the pen tip that makes contact with the writing surface, but located up to an inch away (e.g. inside the shaft of the stylus). As a result, if pen is held at an angle (which is often the case), the X and Y coordinates reported will be off. This is known as parallax caused by pen tilt. Different users may hold the stylus at differing angles, thus requiring the writing surface to be recalibrated each time a different user uses the computing device. Moreover, modifications in one or more configuration parameters may cause systematic disturbances in the EM field, such as the power source of the computer and the usage of drives.
Over time, the user may tire of continually calibrating the writing surface, thereby reducing the desirability of using such a display device. What is needed, therefore, are automated methods and systems of calibrating a pointing device respective to the writing surface during operation of the writing surface that does not require the user to perform a separate calibration process.